Traditionally, devices that perform load balancing among networked servers use software and hardware. The software usually operates to setup and tear down traffic flows, whereas the hardware accelerates the delivery of the traffic. Because of their dependency on the software, such devices cannot achieve line rate (i.e., the nominal speed of data transmission). In general, a device is limited by the speed at which the network processor can process software instructions. In addition, the software often employs a session table to record the states of the traffic flows. Consequently, the number of sessions that the device can process is constrained by the amount of memory installed on the system.
FIG. 1 illustrates traditional server load balancing operation in a data switch module 10 having a network processor 12 that runs a server load balancing agent (hereafter, software SLB agent 14) and a server load balancing processing agent (hereafter, hardware SLB agent 16) that forwards the traffic flows in accordance with the software SLB agent 14. The software SLB agent 14 is in communication with a session table 18 stored in memory 20. Packet traffic from a client system 22 arrives (arrow 1) at the switch module 10. The hardware SLB agent 16 forwards (arrow 2) the packet to the software SLB agent 14. After consulting the session table 18, the software SLB agent 14 returns (arrow 3) a packet to the hardware SLB agent 16. The hardware SLB agent 16 sends (arrow 4) the packet to a server in a server farm 24 (the particular server being selected based on load balancing criteria). A packet returns (arrow 5) from the server farm 24 to the hardware SLB agent 16, which sends (arrow 6) the packet to the software SLB agent 14. The software agent 14 returns (arrow 7) a packet to the hardware SLB agent 16, which sends (arrow 8) the packet to the client system 22. Herein, arrows 1 through 8 correspond to packet traffic for setting up (or tearing down) a session between the client system 22 and the server. After a session is established, the client system 22 and the server in the server farm 24 communicate 26 through the hardware SLB agent 16 (the traffic does not pass through the software SLB agent 14). The performance of the load balancing is limited by the speed at which the software SLB agent 14 can process the packet traffic, and the number of sessions that the system can handle is limited by the amount of memory 20 in the system.